Such flaps are used, for example, in exhaust gas ducts of internal combustion engines in order to regulate the exhaust gas mass flow conveyed through the exhaust gas duct or to generate a counter-pressure for an increase in exhaust gas conveyance in a parallel duct. They are correspondingly used as exhaust gas accumulation flaps, exhaust gas recirculation flaps, or flaps for heat recovery.
Due to the high thermal load in the exhaust gas area, these flap devices are made of materials that are as resistant as possible in order to achieve the longest possible service life. Various concepts have been set forth in recent years for the bearing and sealing of such flaps to the outside. Besides a good tightness to the outside, a growing demand exists for an exact regulation and a good tightness in the closed state of the flap. Abutments for the flap bodies were primarily used in order to achieve a good tightness, the abutments being formed in the duct. However, a problem is this regard exits in that accretions on the shoulders required for that purpose cause the tightness to deteriorate with increasing life span.
For this reason, elliptic flap bodies which abut on the smooth duct walls are increasingly used. In order to avoid a jamming of the flap in the duct, it is necessary to provide abutments in the region not flowed through with which the rotation of the flap body in the duct is limited.
DE 195 26 144 A1, for example, describes an exhaust gas flap which is moved against an internal abutment in the housing to provide a closing that is as tight as possible, and which has an external abutment against which a lever of the flap shaft is moved. Such an arrangement must be manufactured very precisely in order to avoid that, when the flap is closed, the external abutments are formed corresponding to the internal abutments since leakages may otherwise occur at the flap.
This results in the hitherto unsolved problem to provide a long-term tightness of a closed exhaust gas flap. Besides the accretions occurring on the shoulders in the flow housing, thermal expansions of the housings also occur which often differ from those of the flap body or the lever. A jamming of an elliptic flap in an exhaust gas duct is thereby caused since the external abutment is no longer reached at the time the flap body closes the duct. An excessive turning of the flap is instead caused.